1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to an asymmetric error correction device and method thereof, and an optical disc reproducing device using the same. More particularly, the present invention relates to an asymmetric error correction device and method thereof, in which an asymmetric error value is calculated using a 4T sampling signal among digital sampling signals, the calculated asymmetric error value is cumulatively counted to check whether of an asymmetric error, with the result that a signal level is adjusted, and an optical disc reproducing device using the same.
2. Description of the Related Art
With the opening of the multimedia information age, there is a demand for storage and transfer of high-capacity digital data. Accordingly, an optical disc such as a digital versatile disc (DVD) is recently being studied actively. The DVD market has grown due to the computer business trying to employing DVD-ROM (read only memory), and the home electronics industry proposing DVD-Video. Further, optical discs are being expanded in their application fields through the releases of new DVDR (DVD-Writable), DVD-RW (rewritable), and DVD-RAM (random access memory) in the market.
Upon reproducing data recorded on such optical discs as noted above, there occurs a case where waveforms of the analog radio frequency (RF) signals being reproduced become asymmetric. When such asymmetry is present, interference is generated between the reproducing data symbols (inter-symbol interference). If the interference is generated, the detection and correction for a frequency error and a phase error are difficult, causing a problem in that a reproducing signal is distorted. In the conventional optical recording/reproducing system, in order to correct such asymmetric error, a digital sum value (DSV) algorithm was used.
A DSV algorithm is an algorithm that measures DSV to check for an asymmetric error. DSV is a value indicating how much a direct current component is included in a digital signal. Specifically, an optical recording/reproducing system converts an analog RF signal reproduced from an optical disc into a digital sampling signal. Then, a mean value of two digital sampling signals continuously detected is calculated. If the calculated mean value is greater than “0”, the polar value is determined to be “1”, and if the mean value is less than “0”, the polar value is determined to be “−1”. Then, the determined polar value is cumulatively counted, and if the cumulative polar value exceeds a predetermined threshold value, it is determined that an asymmetric error occurs and an input signal is corrected.
However, such a conventional asymmetric error correction method calculates a mean value every digital sampling signal, so that it had a drawback of a slow correction rate. Also, since only a polarity is checked and accumulated using the mean value of the respective sampling signals, there was a problem of reduction in resolution. As a result, for a 4T sampling signal reproduced in a part of variable frequency oscillator (VFO) among the sectors on the optical disc, there was a problem in that a correct asymmetric error cannot be detected.